Writing a New Database Driver (or more?)

[eluser]Unknown[/eluser]
Hey igniters, I'm developing an application with CodeIgniter, but the app won't be using any of the standard drivers. Instead, it will be using CouchDB.

CouchDB strays quite far from the traditional SQL structure. I would like to write a new database driver/plugin/class that can be used in place of the original database object. I like how the current db is integrated in CodeIgniter's code flow; where would I begin to write to achieve this same integration?